Field of the Invention
The present invention relates to a power device. Priority is claimed on Japanese Patent Application No. 2013-119939, filed Jun. 6, 2013, the content of which is incorporated herein by reference.
Description of Related Art
A power system which includes a DC-DC converter, two switches including first and second switches, and two power sources including first and second power sources has been known. The power system switches between a serial connection state where the first and second power sources are connected in series and a parallel connection state where the first and second power sources are connected in parallel based on ON/OFF state of the first and second switches, and connects the first and second power sources in the serial connection state or the parallel connection state with an electrical load, while the power system adjusts a voltage applied to the electrical load using the DC-DC converter (for example, refer to Japanese Unexamined Patent Application, First Publication No. 2012-152079).
A power device which includes a step-up converter, four relays including first to fourth relays, and two secondary batteries has been known. The power device switches between a serial connection state where the two secondary batteries are connected in series and a parallel connection state where the two secondary batteries are connected in parallel based on ON/OFF state of the first to fourth relays, and connects the two secondary batteries in the serial connection state or the parallel connection state with an electrical load, while the power device adjusts a voltage applied to the electrical load using the step-up converter (for example, refer to Japanese Unexamined Patent Application, First Publication No. 2012-60838).
According to the power system and power device of the related art described above, when the power device switches between the serial connection state and the parallel connection state, the first power source (or the secondary battery) is disconnected from the electrical load and step-up and step-down operations are performed only using the second power source (or the secondary battery). Thereby, a voltage needed to be supplied from the second power source (or the secondary battery) is increased. Therefore, it is not easy to control the balance of the voltage supplied from the first power source and that of the second power source (or the secondary batteries).
Moreover, if in addition to the electrical load, a load, which is connected to only the first power source (or the secondary battery), is provided as the power system of the related art described above, there is a possibility that the balance of the voltage supplied from the first power source (or the secondary battery) and that of the second power source (or the secondary battery) is unstable.
The present invention provides a power device which can easily set an arbitrary voltage and easily stabilize a balance of charge and discharge of a first power source and a second power source when the power device controls a voltage applied to a load by switching connection states of the first power source and the second power source for the load.